1. Field of the Invention
This invention relates to an information communication program, an information communication apparatus and an information communication method for communication adapted to use discriminately the address assigned by the connected network and a specific address.
2. Description of the Related Art
The Mobile IP (Internet Protocol) is being used as technique for transferring packets to the destination terminal when the packets are transmitted to the address of the destination terminal but the destination terminal is moving from a network to another. Normally, a terminal that uses the Mobile IP (to be referred to as mobile node hereinafter) has a home address that is an inherent IP address. When the mobile node is located on the home network where it is supposed to be normally found, the packets addressed to the mobile node arrive at the mobile node that is located at the home address.
However, when the mobile node moves to a foreign network that is different from the home network, a care-of address that is an effective IP address on the foreign network is assigned to the mobile node and the corresponding relationship between the home address and the care-of address is registered in the home agent of the home network. With this arrangement, when packets are transmitted to the home address of the mobile node and if it is confirmed that the mobile node that is the addressee of the packets is not located on the home network, the home agent transfers the packets to the addressee mobile node that is found on the foreign network.
The mobile node has the home address as its own IP address and it is normally assumed that some other terminal that transmits data to the mobile node sends out the packets of the data to the home address of the mobile node.
Besides, in addition to the interface by way of which the mobile node communicates (to be referred to as original interface hereinafter), the mobile node has a Mobile IP virtual interface as network interface for the purpose of generating encapsulated packets for the Mobile IP and canceling the encapsulation of the packets.
The prior art that relates to the present invention includes Patent Document 1 [Jpn. Pat. Appln. Laid-Open Publication No. 2002-118596, which proposes an address assigning method for packets in a mobile communication system of the third generation. With the proposed method, when a mobile node is found on a foreign network, the home agent changes the header of the packets to be transmitted to the mobile node and the foreign agent of the foreign network or the mobile node puts the care-of address to the arrived packets. With this arrangement, it is possible to prevent the packets from being refused by the firewall of the network.
However, it is assumed that the packets that are to be received by mobile node are addressed to the home address of the mobile node by way of the Mobile IP virtual interface. This means that, if packets are transmitted to the mobile node from some other terminal on the foreign network, they are transmitted as packets addressed to the home address and the home agent encapsulates and transfers them to the care-of address of the mobile node. In other words, the packets pass through the Mobile IP virtual interface without fail and there exist no packets that are assumed to pass through only the original interface.
When a mobile node is located on a foreign network and some other terminal on the foreign network transmits packets to the mobile node, the terminal transmits the packets to the home address of the mobile node. In other words, the mobile node receives the packets that are encapsulated by way of the home agent. This is because the mobile node is identified only by means of its home address.
In networks where the Mobile IP is installed, the packets to be received by a mobile node are processed by way of the Mobile IP virtual interface of the mobile node without fail. If some other terminal on a foreign network where the mobile node is currently located transmits packets to the care-of address of the mobile node, the Mobile IP virtual interface of the mobile node tries to decapsulate of the received packets to give rise to a problem of discarding packets and/or doing undefined operations.
When the mobile node receives the packets at its own care-of address and then it tries to transmit packets to some other terminal on the foreign network where the mobile node is currently located, the source address of the transmitted packets is that of the home agent so that there arises a problem of disagreement between the address to which the some other terminal transmits packets, which is the care-of address of the mobile node, and the address at which the mobile node receives the packets, which is the home address of the mobile node.
When, on the other hand, the mobile node that is currently located on a foreign network transmits packets to some other terminal on the same foreign network, the packets are transmitted through the Mobile IP virtual interface, encapsulated and then transferred to the some other terminal by way of the home agent. In other words, it is not possible to directly transmit the some other terminal only by way of the original interface.
As described above, it is not possible for an existing mobile node to maintain direct communication with some other terminal while it is moving from a network to another if the some other terminal is always located on a particular network.